The present invention relates to an intermediate product for manufacturing polymers from lignin derivatives which are by-products of the pulp industry, and to the use of these intermediate products in manufacturing highly reactive reagents for making composite materials from plant fibers, waterproof paper and cardboards, and thermosetting plastics from lignin derivatives.
DE 37 992 C2 describes a method for manufacturing a binding agent for wood products, using phenolic substances, in particular lignin sulfonate, whereby enzymes are added to the phenolic substance to activate same, the phenols polymerize according to a radical mechanism, while the phenolic substance is converted into an active binding agent. It is known that this reaction takes place in the presence of oxygen, such as atmospheric oxygen, but until now, such an activated binding agent has not been caused to react with oxygen for a long period of time or by intensive aeration.
Surprisingly it was found that lignin derivatives from the pulp industry, such as kraft lignin or lignin sulfonate, with phenol oxidizing enzymes such as phenol oxidase or laccase, form a particularly reactive lignin product as an intermediate product when caused to react for a long period of time or intensively with oxygen, air or other chemical oxidizing agents. This intermediate product can be isolated and stored for a long time, and it further reacts with other non-activated lignin derivatives to form a polymer of high molecular weight. The intermediate product can be characterized in that the material is caused to react with laccase. After that reaction, it shows a typical ESR spectrum with a signal for phenoxyradicals in the range of about 3400 gauss, which, however, does not remain constant as a typical radical signal. However, surprisingly, the increased reactivity of the intermediate product remains intact even after long periods of time, for example for months. This means that this activated intermediate product is considerably more active when caused to react with phenol oxidizing enzymes than non-treated lignin derivatives, and that the typical ESR spectrum is therefore formed at a considerably higher intensity than lignin derivatives not treated in that manner.
The intensity of the signal of the activated intermediate product is at least five times that of the signal of the lignin derivative serving as the initial product. For example, the signal is measured under the following conditions: 77xc2x0 K.; 9.5 GHz; ESR attenuation 20 dB; mod. frequ. 100 MHz, mod. amplitude 4.0 gauss.
The activated intermediate product can be obtained when technical lignins such as lignin sulfonates, kraft lignin, organosolve lignin, acetosolve lignin, ASAM lignin, etc., which are pulp industry by-products, are treated for a long time with air or oxygen in the presence of phenol oxidizing enzymes. Even after a period of about three hours, for example, but especially after 15 or 20 hours, the phenoxyradical signal can be found to increase. When air or oxygen are passed through under pressure, the increased signal occurs after a significantly shorter period of time, namely after 10 minutes or, as an example, after about 30 minutes.
The intermediate product can also be obtained with chemical oxidizing agents. For example, potassium permanganate, bichromate or ozone, which are customary agents in lignin chemistry, can serve that purpose.
The enzymatic formation of the activated intermediate product is possible only when large amounts of oxygen are present. Since at room temperature, oxygen dissolves in water only at the rate of 9 mg/L, the formation of the intermediate product is encouraged only when more oxygen is added, either through aeration or in the form of oxidation agents. Even when it takes a long time for the oxygen equilibrium to be established, enough oxygen may have acted upon the lignin derivative after some time.
In the presence of phenol oxidizing enzymes, the activated intermediate product reacts with non-activated lignin derivatives that may be obtained, for example, in pulp production. This is accompanied by the formation of polymeric lignin products, whereby the molecular weights are considerably higher than those obtained when phenol oxidizing enzymes act upon lignin derivatives without the presence of activated lignin derivatives. They are generally at least twice as high.
The lignin polymers obtained in the polymerization of lignin derivatives in the presence of active intermediate products can be used for making highly active reagents for the manufacture of composite materials from plant fibers, waterproof papers and cardboards, and thermosetting plastics from lignin derivatives. It is thus possible for the first time to produce fiber-reinforced thermosetting plastics from renewable raw materials completely by in situ polymerization.